The 6xx fields contain various subfields that help patrons find items using keyword and subject searches. The examples below show 650 fields but they are also the same for all 6xx fields including the most commonly used:

600 – personal names (often fictional characters)
651 – geographical terms
655 – genre

Subfields in the subject heading tags further describe the main term in subfield “A”.  

650 #0 $a Scuba diving

V – Form subdivision – to describe the form/genre of the item – fiction, literature, drama, etc.

650 #0 $a Scuba diving $v Fiction.

Y – Chronological Subdivision – to represent a period of time.

650 #0 $a Music $y 500-1400.
650 #0 $a Vocal music $z France $y 18th century.

Z – Geographic subdivision – to represent a specific geographic area.

650 #0 $a World War, 1939-1945 $x Campaigns $z Tunisia.

X – General subdivision – to further describe the subject heading BUT not when these field are more appropriate: $v – Form subdivision, $y – Chronological subdivision, or $z – Geographic subdivision.

650 #0 $a Racetracks $x History.